A top federal health agency announced on Friday that it has determined the standard dose of THC that should be used for marijuana studies moving forward.
The National Institute on Drug Abuse (NIDA) said in a notice to researchers that there is a “new requirement to measure and report results using a standard THC unit in all applicable human subjects’ research,” which is effective immediately. That standard unit is five milligrams of THC.
NIDA said that inconsistencies in measuring and reporting THC exposure “has been a major limitation in studies of cannabis use, making it difficult to compare findings among studies.” Therefore, a “standardized measure of THC in cannabis products is necessary to advance research by providing greater comparability across studies of both its adverse effects and potential medical uses.”
The agency recognized, however, that “the same quantity of THC may have different effects based on route of administration, other product constituents, an individual’s genetic make-up and metabolic factors, prior exposure to cannabis, and other factors.”
But by creating a standard THC dose, it will nonetheless be easier to compare studies that involve THC exposure, which is a “high priority” of NIDA and the National Advisory Council on Drug Abuse.
“It is not the intent of this Notice to prescribe the quantity of THC that is permissible for use in research projects. Indeed, investigators are free to use more or less than 5mg of THC as appropriate for their study,” the notice states. “However, for applicable studies, investigators will be required to report the quantity of THC using the standard unit. Investigators may also report the quantity of THC in other units (e.g., milligrams) as appropriate.”
This comes one year after NIDA, which is part of the National Institutes of Health, first solicited feedback on a proposal to standardize THC content in cannabis research.
The agency said that it carried out “extensive stakeholder input,” along with “consultation with experts in the field,” to arrive at the decision to set the standard unit at 5 mg.
“This guidance will apply to applications where THC is a focus of the research,” the new notice continues. “Applicants are responsible for determining whether use of this standard unit is applicable to their research and for determining best approach to applying it in their research applications. A justification should be provided for research that does not propose to use the standard unit.”
NIDA Director Nora Volkow discussed the importance of establishing a standard THC unit in commentary published in the journal Addiction last year.
Citing research that calls for a five milligram THC standard, Volkow said she agreed with the study’s conclusion despite complicating factors. Those factors include potential issues related to the effect of having cannabis products with the same THC level but different concentrations of other cannabinoids such as CBD.
The complexities in research beyond having a standardized measure of THC “hardly negate the value” of setting one, Volkow said in her commentary. “In fact, having and using such a standard is a prerequisite for comparing the effects of various cannabis products on THC bioavailability, pharmacokinetics and pharmacological effects, which is knowledge fundamental to studies pertaining to medical use of cannabis.”
“Although cannabis remains an illicit substance in the United States, the expanded legalization by states requires us to develop the knowledge base that can help states develop policies to minimize risk from cannabis exposures, such as limits on the THC content of cannabis products,” she said.
Volkow has been vocal about the importance of streamlining and improving research into cannabis, and she’s laid partial blame for the the lack of studies on marijuana’s restrictive federal classification.